Personal care compositions such as skin moisturizing creams, sunscreens, antiperspirants, shampoos, and the like, commonly contain long chain fatty acids and esters. A commonly used linear fatty acid ester in this regard is cetearyl stearate. A commonly used branched fatty acid ester is isocetyl stearate. Such ester materials are useful for providing skin conditioning benefits such as moisturization, humectancy, emolliency, visual improvement of the skin surface, soothing and softening of the skin, improvement in skin feel and the like. Other benefits afforded by long chain fatty acid esters include viscosity and rheology modification.
Cetearyl stearate and isocetyl stearate have different physical characteristics largely due to their differing structural characteristics, namely that cetearyl stearate is a linear fatty acid ester whereas isocetyl stearate is a branched fatty acid ester. For example, cetearyl stearate is typically supplied and shipped as flakes or some other solid form and has a melting point range of about 54° C. to 65° C. This means that it should be converted to a liquid by heating before it can be formulated into personal care compositions. On the other hand, isocetyl stearate, derived from a so-called “Guerbet” alcohol which contains some alkyl branching, is typically liquid at room temperature and has a melting point of about −10° C. The majority of the branching in the “Guerbet” alcohol from which the ester is derived is at the C2 position on the carbon chain. In addition, the alkyl branches tend to be long chain branches, such as C4 and above.
Further, isocetyl stearate is more soluble at room temperature in nonpolar solvents than cetearyl stearate.
Although isocetyl stearate overcomes the solubility problems associated with linear esters of the cetearyl stearate type, it is unfortunately relatively difficult to manufacture. Firstly, a Guerbet alcohol has to be produced which involves the preparation of an aldehyde followed by an aldol condensation. It would therefore be desirable to provide an ester compound which ameliorates the solubility problems of linear esters such as cetearyl stearate, while at the same time being easier to manufacture than esters derived from branched Guerbet alcohols.
Further, from the viewpoint of improving formulation flexibility, it would be desirable to provide a long chain ester having physical properties in between that of the linear cetearyl stearate type ester and the branched isocetyl stearate type ester. In particular it would be desirable to provide a long chain ester having a physical form which is somewhere in between a solid flake and a homogeneous liquid, and having a melting point intermediate of that of cetearyl stearate and isocetyl stearate. In addition to affecting handling characteristics in commercial settings, the melting point properties of esters used as emollients have been related to the resulting skin feel of the product, with fully liquid emollient ingredients providing a “light” skin feel while solid emollient ingredients result in a “heavy, long-lasting” skin feel.
It has now surprisingly been found that the particular branched ester composition of the present invention which is derived from a branched primary alcohol composition having from 0.7 to 3.0 branches per molecule said branching comprising methyl and ethyl branches has physical properties which are intermediate between cetearyl stearate and isocetyl stearate type esters. This is advantageous for providing an improvement in formulation flexibility. In addition, it has surprisingly been found that the branched ester composition of the present invention helps to overcome the problems of high melting points and low solubility associated with the linear cetearyl stearate type esters while at the same time being easier to manufacture than the branched isocetyl stearate type esters derived from Guerbet alcohols.
U.S. Pat. No. 5,849,960 (Shell Oil Company) discloses a branched primary alcohol composition having from 8 to 36 carbon atoms which contains an average number of branches per molecule of at least 0.7, said branching comprising methyl and ethyl branching. These alcohols can subsequently be converted to anionic or nonionic detergents or general surfactants by sulfonation or ethoxylation, respectively, of the alcohol. The detergents produced exhibit useful properties such as high biodegradability and high cold water detergency. No disclosure is provided in U.S. Pat. No. 5,849,960 of esters derived from these alcohols, nor the use of these branched alcohols or esters derived therefrom in personal care compositions.
Co-pending U.S. patent application Ser. No. 60/407,724 discloses the use of such alcohols as emollients in personal care compositions.
WO99/18929, WO99/18928 and WO97/39089 (The Procter and Gamble Company) disclose personal cleansing compositions comprising mid-chain branched surfactants. The mid-chain branched surfactants are manufactured from mid-chain branched alcohols. The formulations therein however do not contain any mention of esters derived from these mid-chain branched alcohols per se, only the corresponding surfactants. In addition, these documents are concerned with cleansing compositions having relatively high levels of surfactant ingredients.